Implementing backdrilling elimination utilizing via plug during electroplating

ABSTRACT

A method and structure are provided for implementing enhanced via creation without creating a via barrel stub. The need to backdrill during printed circuit board (PCB) manufacturing is eliminated. After the vias have been drilled, but before plating, a via plug with a specialized geometry and including a capillary is inserted into each via to allow electroplating on only preferred wall surfaces of the vias. Then a board plating process of the PCB manufacturing is performed.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method and structure forimplementing manufacture of a printed circuit board (PCB) with enhancedvia creation without creating a via barrel stub, eliminating the need toback-drill.

DESCRIPTION OF THE RELATED ART

The computer hardware development industry has reached a point whereinmany computer interfaces are of sufficient switching speed as to requiresignal routing layer change vias to be back-drilled to remove via barrelstubs. Backdrilling is a conventional technique used to remove the viabarrel stub. Without removal of the unnecessary section or length of avia barrel, some amount of the propagating signal is reflected away fromthe intended receiver, thereby significantly reducing the amount oftotal energy effectively transferred from driver to receiver.

While there are known processes to mechanically remove these stubs, onceback-drilled, it is no longer possible to probe those locations on theprinted circuit board (PCB), cost of the PCB increases substantially,and success of the process is statistically less than ideal. These factssignificantly complicate our ability to manufacture cost-effective PCBs,measure high-speed interfaces in the lab during system bring-up andmodel-to-hardware correlation activities, and maximize the electricalperformance of our computer interfaces. When system errors occur in thefield, the field engineer cannot measure and confirm function at thesePCB via locations while at the customer's site.

A need exists for a method and structure for implementing via creationthat eliminates creation of a via barrel stub, eliminating the need toback-drill, reducing PCB cost, and maximizing interface margin.

As used in the following description and claims, the term printedcircuit board (PCB) should be understood to broadly include a printedwiring board or other substrate, an interconnect substrate, and varioussubstrates including a plurality of insulator layers, and internalconductive traces.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide a method andstructure for implementing manufacture of a printed circuit board (PCB)with enhanced via creation without creating a via barrel stub,eliminating the need to back-drill. Other important aspects of thepresent invention are to provide such method and structure substantiallywithout negative effects and that overcome many of the disadvantages ofprior art arrangements.

In brief, a method and structure are provided for implementing enhancedvia creation without creating a via barrel stub. The need to backdrillduring printed circuit board (PCB) manufacturing is eliminated. Afterthe vias have been drilled, but before plating, a via plug with aspecialized geometry and including a capillary is inserted into each viato allow electroplating on only preferred wall surfaces of the vias.Then a board plating process of the PCB manufacturing is performed.

In accordance with features of the invention, the via plugs are formedof a selected electrically insulating material.

In accordance with features of the invention, the via plug with thecapillary prevents the electroplating from creating via barrel stubs,thus eliminating the need to backdrill each via after the platingprocess.

In accordance with features of the invention, the via plugsadvantageously have beneficial effects on signal integrity and noisereduction due to their insulative properties and the via plugs remain inthe board after plating

In accordance with features of the invention, eliminating back-drillingimproves yield and late fail discoveries, both of which can improve costand reliability of boards.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIG. 1 illustrates an example structure for manufacturing a printedcircuit board (PCB) with enhanced via creation without creating a viabarrel stub, eliminating the need to back-drill in accordance with thepreferred embodiment;

FIG. 2 is a flow chart illustrating example steps for implementing astructure embodying the enhanced via creation without creating a viabarrel stub in accordance with the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings, which illustrate exampleembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In accordance with features of the invention, a method and structure areprovided for implementing enhanced via creation without creating a viabarrel stub. The need to backdrill vias during printed circuit board(PCB) manufacturing is eliminated. After the vias have been drilled, butbefore plating, a via plug is inserted into each via. The via plug has aspecialized geometry and a capillary allowing electroplating on only thepreferred surfaces of the via.

In accordance with features of the invention, the PCB plating process isperformed using a conventional plating process. Conventional PCBfinishing processes are performed, advantageously eliminating the needto backdrill each via after the plating process.

In accordance with features of the invention, the via plug is formed ofa selected electrically insulating material.

In accordance with features of the invention, an arrayed tool optionallyis used to insert multiple plugs or groups of plugs all at once. The viaplugs provide enhanced signal integrity and noise reduction due to theirelectrically insulative properties and the via plugs optionally remainin the board after plating.

Having reference now to the drawings, in FIG. 1, there is shown anexample structure generally designated by reference character 100 formanufacturing a printed circuit board (PCB) with enhanced via creationwithout creating a via barrel stub, eliminating the need to back-drillin accordance with the preferred embodiment.

Structure 100 includes a printed circuit board (PCB) 102 having aninternal conductive or signal trace 104. PCB 102 includes an insulatorsubstrate or insulator layers, with one or more internal conductivetraces 104. Structure 100 includes a via 106 extending through theprinted circuit board (PCB) 102 and the internal conductive trace 104.Structure 100 includes a via plug 108 including a capillary 110extending through the via plug. The via plug 108 with the capillary 110eliminates via barrel stub creation during a PCB plating process duringPCB manufacturing.

The via plug 108 is formed of an electrically insulating material havingsufficient strength and rigidity for insertion into the via 106. The viaplug 108 has a specialized geometry and a capillary 110 allowingelectroplating on only the preferred surfaces of the via. The via plug108 has a specialized geometry conforming to the via 106 enabling thevia plug to be slidingly received within the via 106. As shown, the viaplug 108 is a cylindrical via plug fabricated with a capillary 110 suchthat when plugged into a via 106, the via plug allows fullelectroplating of the inner surface of the via, but prevents anyexcessive plating that would reduce signal integrity. The via plug 108presents an inexpensive and quick method of improving a boards signalperformance while also reducing the amount of electroplating required.

The via plug 108 with the capillary 110 prevents the PCB plating processfrom creating via barrel stubs, thus eliminating the need to backdrilleach via after the plating process Eliminating back-drilling improvesyield and late fail discoveries, both of which can improve cost andreliability of boards.

In accordance with features of the invention, the printed circuit board(PCB) 102 and via 106 are formed generally including standard PCBmanufacturing processes, including via drilling and plating. However,the step of back-drilling at the end is removed and the PCB process ofthe invention provides that after the vias 106 have been drilled, butbefore plating, a small via plug 108 is inserted into each via 106. ThePCB 102 is then sent through the normal plating process. The via plug108 prevents the plating from taking hold in the area that via plug 108occupies, and eliminates creation of the via barrel stub eliminating theneed to backdrill each via after the plating process.

Referring now to FIG. 2, there is shown a flow chart illustratingexample steps generally designated by reference character 200 forimplementing a structure embodying the enhanced via creation withoutcreating a via barrel stub in accordance with the preferred embodimentstarting at a block 202.

As indicated at a block 202, a lamination is formed defining the PCB 102and at least one internal conductive traces 104.

As indicated at a block 204, vias 106 are drilled. Conventional viadrilling is performed.

As indicated at a block 206, the via plugs 108 having the capillary areinserted into the vias 106. The capillary 110 in via plug 108 provides aregion for any fluid to escape and proper filling of the via hole 106,preventing any electroplating from crossing in to the undesirableregions of the via 106 and PCB 102, and eliminates creation of the viabarrel stub.

As indicated at a block 208, the PCB plating process is performed, usinga conventional plating process. It should be understood that either thevia plugs 108 remain in the PCB 102 or optionally are removed after thePCB plating process is performed.

As indicated at a block 210, conventional PCB finishing processes areperformed, advantageously eliminating the need to backdrill each viaafter the plating process.

In accordance with features of the invention, the alternative method forvia creation eliminates creation of the via barrel stub. Since the viabarrel stub is not created, the need to back-drill is eliminated,reducing PCB cost and maximizing interface margin.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

1. A method for implementing enhanced via creation without creating avia barrel stub during printed circuit board (PCB) manufacturingcomprising: providing a printed circuit board (PCB); said printedcircuit board (PCB) having an internal conductive trace; forming a viaextending through the printed circuit board (PCB) including the internalconductive trace; inserting a via plug into the via, said via plughaving a capillary extending through said via plug; and performing PCBplating.
 2. The method as recited in claim 1 includes said via plugremaining in the PCB via after PCB plating.
 3. The method as recited inclaim 1 includes providing enhanced signal integrity with said via plug.4. The method as recited in claim 1 includes providing enhanced noisereduction with said via plug.
 5. The method as recited in claim 1includes forming with said via plug with a selected electricallyinsulating material.
 6. The method as recited in claim 1 whereininserting a via plug into the via includes slidingly inserting said viaplug into the via.
 7. The method as recited in claim 1 includes formingwith said via plug with a specialized geometry and capillary conformingto the via.
 8. The method as recited in claim 1 wherein providing aprinted circuit board (PCB); said printed circuit board (PCB) having aninternal conductive trace includes a standard PCB manufacturing process.9. The method as recited in claim 1 wherein inserting said via plug intothe via includes providing an arrayed tool used to insert multiple onesof said via plugs at once.
 10. The method as recited in claim 1 includesperforming a standard PCB plating process responsive to inserting thevia plug.
 11. The method as recited in claim 1 includes performingconventional PCB finishing processes with aid via plug remaining in thePCB via after PCB plating.
 12. The method as recited in claim 1 whereineliminating via back-drilling enables improved yield and reliability ofthe PCB. 13-20. (canceled)